1. Field
One or more embodiments relate to an image-registration method, medium, and apparatus, and, more particularly, to an image-registration method, medium, and apparatus in which image registration can be stably performed at high speed even on images having very different properties by using image pyramids and reducing the amount of computation required to calculate objective functions for each level of the image pyramids.
2. Description of the Related Art
Image registration is a process of geometrically matching two or more images that are physically similar to one another on a region-by-region basis.
In recent years, various image registration techniques have been suggested that are capable of generating high dynamic range (HDR) images, performing image registration for the purpose of motion deblurring or performing image registration on various types of images (e.g., an image captured by a typical camera and an image captured by an infrared camera, or a computed tomography (CT) image and a magnetic resonance imaging (MRI) image) captured by different image-capturing apparatuses with different modalities.
Conventional image-registration methods using a luminance-based method can be applied only to images obtained under similar photographing conditions (such as luminance or motion blur). Images obtained under different photographing conditions are highly likely to have very different properties from each other. If two images for which image registration is to be performed have very different properties from each other, motion estimation for the two images may not be able to be properly performed. For example, in the case of generating an HDR image by performing image registration on two images obtained from different exposure times, edge information of very bright or very dark regions in the two images is highly likely to be lost especially when there is a huge difference between the luminance levels of the two images. In addition, in the case of performing multiple exposure-based motion deblurring on two images obtained from different exposure times, image registration may not be able to be properly performed because the amount of motion blur varies from one image to another due to the different exposure times.
Conventional image-registration methods using a probability-based method such as mutual information or normalized mutual information can enhance the stability of image registration even when images have very different properties from each other, but are not suitable for use in camera systems that operate online because of their considerable amounts of computation.